Free piston apparatus

ABSTRACT

A by-pass including a heat regenerator is provided for a cylinder in which an oscillating free piston of a gas pump is driven. Shunting of gas back and forth through the by-pass between disparate hot and cold regions of the cylinder while the piston coasts in the by-pass region produces a periodic temperature and pressure variation which may be applied to a load. In one embodiment the by-pass includes in seriatim cold, regenerator, and hot chambers. In another embodiment the heating and/or cooling means are located within the cylinder. In still another embodiment preheated gas is drawn through an inlet into the hot end portion of the cylinder, and cool gas is drawn into the cool end portion of the cylinder. In one embodiment piston oscillation is sustained by means of a thermal leg chamber included in the piston. In another embodiment pressure pulses are fed back to the cylinder to sustain oscillation. In one embodiment the amplitude and frequency of pump pressure variations are controlled by varying the coasting portion of the cycle. In another embodiment the pump output is controlled by shunting a variable amount of gas around the heater and/or around the cooler, or to a second by-pass containing only a regenerator. In a further embodiment, the pressure variations are controlled by varying the feedback of pressure pulses. In still another embodiment pumping is controlled by varying the geometry of a thermal lag chamber or the portion of the cycle during which it is operative. Variations in temperature or geometry of pump components are also used as pump control means in certain embodiments. In one embodiment the pump produces electrical power by driving a free piston linear alternator wherein pumping controls such as the above can be used to maintain relatively constant voltage and frequency under conditions of variable load. In another embodiment the pump may be used to pump gases from one region to another, or from one pressure to another. In a further embodiment the pump may be used as a cooling device. In certain embodiments the pump may be used to produce pressure variations in a medium. In embodiments utilizing a thermal lag chamber for sustaining oscillation of the free piston, the relatively little coupling between the load and the free piston results in a pump which is essentially stall-free.

United States Patent [191 Schuman 1 Jan. 1, 1974 [5 FREE PISTON APPARATUS Mark Schuman, 101 G St., S.W., Washington, DC.

[22] Filed: Dec. 7, 1971 [21] Appl. No.: 205,651

Related US. Application Data [76] Inventor:

[52] US. Cl 417/207, 60/24, 417/375 [51] Int. Cl. F04b 19/24 [58] Field of Search 60/24; 417/207, 375

[56] References Cited UNITED STATES PATENTS 3,563,028 2/1971 Goranson et a1. 60/24 3,552,120 1/1971 Beale 60/24 3,525,215 8/1970 Conrad 60/24 3,484,616 12/1969 Baumgardner et al. 60/24 3,559,398 2/1971 Meijer et al. 60/24 3,583,155 6/1971 Schuman 60/24 3,604,821 9/1971 Martini 60/24 3,597,766 8/1971 Buck 60/24 3,608,311 9/1971 Roesel 60/24 Primary ExaminerWilliam L. Freeh Assistant Examiner-Gregory LaPointe AttorneyLowe and King [57] ABSTRACT A by-pass including a heat regenerator is provided for a cylinder in which an oscillating free piston of a gas pump is driven. Shunting of gas back and forth through the by-pass between disparate hot and cold regions of the cylinder while the piston coasts in the by-pass region produces a periodic temperature and pressure variation which may be applied to a load. In one embodiment the by-pass includes in seriatim cold,

regenerator, and hot chambers. In another embodiment the heating and/or cooling means are located within the cylinder. in still another embodiment preheated gas is drawn through an inlet into the hot end portion of the cylinder, and cool gas is drawn into the cool end portion of the cylinder. In one embodiment piston oscillation is sustained by means of a thermal leg chamber included in the piston. in another embodiment pressure pulses are fed back to the cylinder to sustain oscillation. ln one embodiment the ampli tude and frequency of pump pressure variations are controlled by varying the coasting portion of the cycle. In another embodiment the pump output is controlled by shunting a variable amount of gas around the heater and/or around the cooler, or to a second by-pass containing only a regenerator. In a further embodiment, the pressure variations are controlled by varying the feedback of pressure pulses. in still another embodiment pumping is controlled by varying the geometry of a thermal leg chamber or the portion of the cycle during which it is operative. Variations in temperature or geometry of pump components are also used as pump control means in certain embodiments. in one embodiment the pump produces electrical power by driving a free piston linear alternator wherein pumping controls such as the above can be used to maintain relatively constant voltage and frequency under conditions of variable load. In another embodiment the pump may be used to pump gases from one region to another, or from one pressure to another. In a further embodiment the pump may be used as a cooling device. In certain embodiments the pump may be used to produce pressure variations in a medium. In embodiments utilizing a thermal lag chamher for sustaining oscillation of the free piston, the relatively little coupling between the load and the free piston results in a pump which is essentially stall-free.

119 Claims, 17 Drawing Figures PATENTED JAN 1 7 SHEET S (If 7 FREE PISTON APPARATUS RELATIONSHIP TO COPENDING APPLICATIONS The present application is a continuation-in-part of my copending application entitled Free Oscillating Piston Apparatus, Ser. No. 169,003 filed Aug. 4, 1971, now abandoned and is an improvement on my copending application entitled Oscillating Piston Apparatus, Ser. No. 121,371, filed Mar. 5, 1971 now abandoned.

FIELD OF INVENTION The present invention relates generally to free oscillating piston devices for converting externally applied thermal energy into work or another form of energy and, more particularly, to a free oscillating piston apparatus wherein the piston coasts in a by-pass region of a cylinder, which by-pass includes a regenerator.

BACKGROUND OF THE INVENTION Efficient free piston devices including the principles of a Stirling engine have been reported. A free piston is one having no mechanical coupling to drive sources outside of the cylinder in which it travels. One of the reported devices is a regenerative device wherein a working gas is forced through the series combination of a heater, regenerator and cooler by a displacer piston that moves relative to a working piston in a cylinder. In this device the free piston is a combination of the displacer and working pistons. The use of a displacer piston that moves relative to a working piston obviates some of the inherent advantages of a free piston, namely, the simplicity, low friction, and low wear typically resulting from the use of only a single moving member in each cylinder. The coupling and contact between the displacer and working pistons during each cycle of the reported device absorb energy to reduce efficiency. In addition, contact between the displacer and working piston may have a tendency to produce unwanted vibrations. Further, the coupling between the displacer and working pistons makes the device more susceptible to being stalled by a severe load.

Other modern free piston regenerative devices include a free piston that is divided into a displacing and reversing pistons which are rigidly interconnected to each other. In response to varying differential pressure against its faces, the reversing piston changes its direction of movement and that of the displacer piston also. The displacing and reversing pistons do not ride in exactly the same cylinders, and do not always see the same pressures. During at least a portion of the cycle the reversing is done concurrently with the displacing, and the energy for reversing is derived from the pump output. The free piston of these devices is of a relatively complex shape and therefore difficult to fabricate. It is also susceptible to stalling.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, a regenerator is incorporated in an efficient piston device wherein a single, free piston is oscillated in each pump cylinder. Each cylinder is divided into first and second variable volume chambers by the opposite faces or edges of the single piston. The single piston, which is preferably of simple cylindrical shape, functions as both a displacer piston and as a reversing piston during different portions of an oscillating cycle. A by-pass, including the regenerator, is established around the piston faces between thefirst and second chambers while the piston is moving through a center region of the cylinder between the ends thereof. Thereby, gas in the cylinder flows through the by-pass from the first chamber to the second chamber while the piston is moving through the central region in a direction tending to increase the volume of the second chamber and decrease the volume of the first chamber. When the piston is moving through the central region in the opposite direction, so that the volume of the first chamber is increasing and the volume of the second chamber is decreasing, gas flows through the by-pass from the second chamber to the first chamber. The by-pass is blocked twice during each cycle of piston oscillation after the piston has coasted through the central region of the cylinder. Gas flowing into the second chamber through the by-pass is cooled while the piston is moving through the central region in a direction to increase the volume of the sec ond chamber. Gas flowing into the first chamber through the by-pass while the piston is moving through the central region in the opposite direction is heated.

The regenerator is a heat storage and release mechanism, whereby during each cycle heat is applied to the cool gases and withdrawn from the hot gases flowing through the by-pass. The regenerator enables the temperature and pressure of the cooled gas to increase before the gas is heated by externally applied heat while flowing from the second chamber through the by-pass to the first chamber during a portion of one half cycle of the piston oscillation through the center region of the cylinder. Conversely the regenerator enables a decrease in the gas pressure to occur before the gas is cooled in an externally cooled cooling chamber during the opposite half cycle of the piston travel through the central region of the cylinder. The by-pass is also important to enable the center position of the oscillating free piston to be established in a manner similar to that disclosed in my co-pending application entitled Oscillating Piston Apparatus, filed Mar. 5, 1971.

Oscillation of the free piston can be sustained by utilizing previously developed passive thermal lag techniques, such as disclosed in my U. S. Pat. No. 3,489,335, issued Jan. 13, 1970, or as disclosed in my aforementioned co-pending applications. In addition, the free piston can be driven from other energy sources, e. g., a pressurized source of gas. In accordance with one embodiment of the present invention, the gas source is pressurized by a feedback arrangement from the pump outlet.

To minimize vibration, in accordance with several embodiments of the invention, a pair of free oscillating pistons and a pair of cylinders are provided. The free oscillating pistons are driven in synchronism with each other so that the net vibration of the entire structure is virtually zero.

In accordance with another aspect of the invention, in certain embodiments thereof, the free piston or pistons are the only moving parts. Thereis no need for valves to control the flow through theby-pass because the free, oscillating piston and the by-pass are dimensioned in such a manner as to enable the piston itself to selectively block and unblock the by-pass.

Another feature of the invention is that most load variations are incapable of stalling the free, oscillating piston. The load is connected to the cylinder through a port which is in general positioned in the second chamber in such a manner as to be responsive to cooled gas while the piston is coasting through the central portion of the cylinder. The load is responsive to the cooled gas in the second chamber primarily while the piston is coasting in the central region while the by-pass is unblocked. Since the by-pass is unblocked, load variations have substantially the same effect on both sides of the coasting piston and usually cannot stall the coasting piston.

In accordance with another aspect of the present invention, power modulation can be performed quickly, easily, over a wide range of values, and with a relatively high degree of accuracy when the free piston device is connection as an oscillatory pressure source driving a load. Thereby, the amount of power supplied to the load and the frequency of pressure variation can be controlled.

Power and frequency control can be achieved by varying the length and position of the by-pass region through which the free oscillating piston coasts in a cylinder. Increasing the length of the by-pass region, which increases the coasting time of the piston through the by-pass region, results in a greater output power being supplied by the oscillating piston pump to the load. Conversely, decreasing the length of the coasting region, which decreases the amount of time during which gas is supplied to the load by the pump, results in the application of a lesser amount of power to the load. Changing the by-pass length changes the mass of gas forced through the by-pass and heated or cooled thereby. Therefore, the amount and time duration of pressure variation applied to a load are changed. If heating and cooling chambers in the by-pass are heated and cooled at a sufficient rate while the by-pass is relatively short, appreciable heat energy is stored in the chamber walls because there is a relatively low gas flow through the bypass. The stored energy in the chamber walls is available for rapid conversion into pneumatic power in response to the length of the by-pass region increasing. Efiiciency is considerably greater at low power levels than would be attained with conventional flow modulation techniques, e.g., restricting flow by a valve.

There is a tendency for changes in the by-pass length or position to effect the frequency of piston oscillation. In my devices employing pneumatic springs at the ends of the cylinder to reverse the direction of piston movement, as disclosed in my co-pending applications, the effects on piston oscillation frequency due to changes in the by-pass length have a tendency to be cancelled. This is because changing the length of the by-pass tends to change the pressures at the ends of the cylinders which alters the pneumatic spring constants of gases at the ends of the cylinders. The alteration in spring constants is offset to a certain extent by the change in coasting time of the piston through the cylinder by-pass region. If the load to be driven requires precise frequency regulation, a frequency controlled system can be provided by responding to the load frequency and varying the location of the by-pass orifices or other changes in pump geometry in order to vary the pressure, spring constants or coasting time.

An additional aspect is a free piston electrical alternator responsive to oscillatory or periodic pressure variations such as may be derived from the free piston pump. Such a combination results in a thermally driven alternator which is sealed and which can automatically maintain substantially constant voltage and frequency under variable load conditions. The alternator portion comprises a magnetic circuit including magnetic poles displaced along the walls of the alternator cylinder. One component of the magnetic circuit is the free, oscillating piston driven by the periodic pressure variations. The magnetic circuit also includes coil means magnetically coupled through the alternator cylinder walls to the free piston, whereby there is induced an ac. voltage in the coil means in response to the free piston being driven. The free piston may include poles of a permanent magnet, or the free piston can be of a material having high magnetic permeability coupled to pole faces in or outside of the cylinder walls. The alternator piston could have a by-pass for maintaining its desired center of oscillation in spite of variable pressure and load, but not for heating or cooling gases in the by-pass as in the case of the pump.

In accordance with another aspect of the present invention, a free oscillating piston in a cylinder including a by-pass having a heater is responsive to an external source of cool gas or gas from an external source as fed to the cool end cylinder through a cooling chamber. By using cool gas or by cooling gas from an external source prior to supplying it to the cylinder, a cooling chamber in the by-pass becomes less important and can even be eliminated. Heating, as well as cooling, may similarly be derived from gases being pumped.

In accordance with still a further embodiment of the invention, a thermal lag heater to sustain piston oscillation comprises hot passageways in the face of the piston communicating with the cold end of the cylinder. The piston and, therefore, the passageway walls are heated by hot gases from the by-pass and by radiant and conductive heat transfer from the hot cylinder walls.

In accordance with an additional embodiment, at least one controlled flow shunt path is provided around the heating and cooling chambers in the by-pass to control the amount of heating and cooling in the by-pass, and thus the average and differential pump pressure. In one arrangement, separate variable shunt flow paths are provided around the hot and cold chambers of the by-pass. In a second arrangement, another regenerator is provided in a variable shunt flow path around the hot, regenerator and cold chambers in seriatim. The first arrangement is particularly advantageous since oscillating frequency and output power can be controlled independently by varying the amount of heating and cooling individually.

In accordance with another aspect of the invention, modulation is achieved by varying one or more properties of the thermal lag device. To this end, the geometry, e.g., volume or passageway shape, of the thermal lag device can be controlled or theportion of the cycle over which the thermal lag device is operative can be controlled.

It is, accordingly, an object of the present invention to provide a new and improved free oscillating piston apparatus.

It is another object of the present invention to provide a new and improved simple and efficient free oscillating piston pump utilizing a heating chamber, regenerator, and cooling chamber.

Another object of the invention is to provide a new and improved free oscillating piston device having a minimum amount of vibration.

Another object of the invention is to provide a new and improved, efficient, free oscillating piston pump having as its only moving part a piston which functions alternately as a displacer and a reversing piston.

A further object of the invention is to provide a free oscillating piston energy conversion device employing a regenerator connected in a bypass around the piston, which by-pass also functions to determine the approximate center of piston oscillation. 105. An additional object of the invention is to provide an improved free, oscillating piston energy conversion device which is relatively insensitive to load variations and is path beginning stallfree.

Another object of the present invention is to provide a new and improved free oscillating piston device wherein the amount of power derived from the device can be varied rapidly in a simple manner.

Another object of the invention is to provide new and improved devices for rapidly controlling the oscillation frequency of a free piston device.

A further object of the invention is to provide a free oscillating piston device wherein power and frequency are controlled by varying the coasting of a piston in a cylinder containing a by-pass, which by-pass includes a regenerator and possibly a cooler and/or heater.

An additional object of the invention is to provide a new and improved, pressure driven, linear alternator employing a free piston which is centered in its cylinder in a simple, reliable manner.

Another object of the invention is to provide a new and improved system wherein an oscillating free piston pump drives and accurately controls an oscillating free piston linear alternator under conditions of variable load.

Yet another object of the invention is to provide a new and improved system for driving an electrical load in response to current derived from an alternator including free, oscillating pistons driven by oscillatory pressure variations derived from an oscillatory pressure source.

A further object of the invention is to provide a free oscillating piston pump that is controlled in power and frequency by varying the amount of heating and/or cooling of gas flowing in a by-pass.

Another object of the invention is to provide a new and improved, highly efficient and simply constructed free piston energy converter wherein oscillation of the free piston is sustained and controlled by a thermal lag means.

An additional object of the invention is to provide a free oscillating piston pump that is controlled by varying, during its cycle, the mass flow rate of gas through a by-pass.

A further object of the invention is to provide a new and improved thermally driven pump wherein the ther' mal energy to operate the pump is derived in part or in full from the fluid or fluids being pumped.

An additional object of the invention is to provide a new and improved cooling apparatus employing a free piston regenerative cycle device.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of several specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of one embodiment of the present invention employing a single piston and a thermal lag heater to sustain oscillation;

FIG. 2 illustrates pressure vs. displacement curves for the device of FIG. 1 when the outlet is closed:

FIG. 3 is a schematic diagram of a modification of FIG. 1, wherein a pair of synchronized pistons is provided to cancel vibration and a loose piston is employed as a starter;

FIG. 4 is a modification of the pump of FIG. 3, wherein cylinders carrying the synchronized pistons communicate with each other via a thermal lag heater, heating and cooling chambers are provided in the cylinders, and the connections to a load are illustrated;

FIG. 5 is a modification of the system of FIG. 4, wherein heating and cooling means are provided only in the cylinders and alternative load connections are illustrated;

FIGS. 6 and 7 are other synchronized piston embodiments wherein oscillation is sustained by pressure feed back from a load;

FIG. 8 is a diagram of an embodiment wherein pressure variations supplied to a load are affected by con trolling the coasting region of the free piston and wherein a free piston alternator is responsive to oscillatory pressure variations;

FIG. 9 is a diagram of a modification of the system of FIG. 8, wherein a separate pump inlet and outlet are provided and gas entering the pump through the inlet is precooled;

FIG. 10 is a diagram illustrating how the device of FIG. 9 can be modified so that there is no cooling chamber in the by-pass and also illustrates how the os cillating piston pump may utilize two synchronized free pistons;

FIG. 11 is a diagram of an embodiment employing a thermal lag heater carried by the free piston;

FIGS. l2, l3 and 14 are diagrams of further embodiments wherein pressure amplitude and frequency are controlled by varying the amount of heating and cooling of gas flowing in the by-pass;

FIG. 14 also illustrates two thermal lag chambers having variable propertiesfor varying piston amplitude and frequency.

FIG. 15 illustrates how the present invention may be employed for cooling or warming a remote body.

FIG. 16 illustrates how the present invention may be used as a heat pump or refrigerator.

FIG. 17 is a diagram illustrating another embodiment of the invention for transforming pressure variations.

DETAILED DESCRIPTION OF THE DRAWING.

Reference is now made to FIG. 1 of the drawing wherein there is illustrated a gas pump including a sealed cylinder 11 through which free piston 12 is oscillated. The opposite faces of piston 12 divide cylinder 1l into a first and second chamber 13 and 14. At the end of chamber 14 there is provided a series of elongated passageways 15 located in a double walled chamber 10. A heating source 16 extends between the interior walls of chamber 10 so that passageways 15 are heated to establish a thermal lag heating chamber to sustain oscillation of piston 12. As described in my application filed Mar. 5, 1971, passageways 15 may be heated along their lengths, and the: cylinder walls may be cooled in proximity to conduit 17, and cooling fins may be added. Cooling chamber 23 also contributes to cooling of the gases in chamber 14. The cooling of gases in chamber 14 augments the subsequent heating of these gases upon the gases being forced by piston 12 into the heated passageways 15. Thus the cooling of gas in chamber 14, as well as the heating of passageways 15, increases the kinetic energy supplied to piston 12 by the thermal lag heating chamber 10, and this increase in kinetic energy tends to increase the piston amplitude and frequency.

The walls of cylinder 11 and piston 12 are so close to each other that the piston provides a reasonably good seal between the opposite faces thereof. Therefore, while piston 12 is near the top and bottom respectively of chambers 13 and 14, there is a substantial difference between gas pressures at opposite faces of the piston. In a central region of cylinder 11, the pressure difference across piston 12 is virtually zero due to a by-pass formed by lines 18 and 19, between which are connected in seriatim heater 21, regenerator 22 and cooler 23. Heater 21 can be a chamber containing one or more heated passageways, regenerator 22 can be a chamber containing a mesh of wire through which gas flows between heater 21 and cooler 23, and cooler 23 can be a chamber containing one or more passageways and having cooling fins or other means for external cooling.

Orifices 1 and 2 are positioned in the side wall of cylinder 11 leading to conduits 18 and 19 and the length of piston 12 is determined in such a manner that both conduits simultaneously communicate with chambers 13 and 14 while piston 12 is coasting in the cylinder central region between the orifices. The positions of orifices 1 and 2 and the length of piston 12 are such that the piston covers and blocks conduit 18 when the volume in chamber 13 is a minimum and for a certain time interval on either side of minimum volume, and the piston blocks conduit 19 while the volume in chamber 14 is a minimum and for a certain time interval on either side of minimum volume. Chambers 13 and 14 (the volume of chamber 14 includes the volume of passageways 15) form gaseous springs at each end of cylinder 11. The upper gaseous spring is not'always effective during piston start up, however, whereby a resilient stop 24 may be provided at the end of chamber 13 to guarantee a minimum amount of gas for this gaseous spring.

A load 25 is driven by pressure variations in the cylinder 11 through a conduit 26 having an orifice 3 disposed in the side wall of cylinder 11 approximately the same distance from the lower end of cylinder 11 as orifice 2 so that orifices 2 and 3 are open and closed at about the same time. Thereby, as piston 12 coasts between orifices l and 2 in a downward direction, compressed gas is fed through conduit 26 to load 25 at relatively high pressure and substantially no gas is fed to conduit 26 while the lower face of piston 12 is below orifices 2 and 3. Gas is drawn from the load 25 at relatively low pressure while the piston 12 is moving upward above the orifices 2 and 3. If the gas drawn from the load is cool, it assists in cooling the gas in chamber 14.

While the orifice feeding pressure variations from the pump to load 25 is preferably in the position illustrated to substantially prevent stalling, it is to be understood that the orifice in this and other embodiments can be located at other positions.

A suitable starting means 55-58 for piston 12, as described in my previously mentioned copending applications as is described herein infra, can be employed. To describe the operation of the embodiment of FIG. 1, it is initially assumed that piston 12 is at its greatest upward travel to minimize the volume of chamber 13 and close off orifice 1. To simplify the operating description, it is assumed that orifice 26 is blocked so that load 25 has no effect on operation. With piston 12 so located, the inlet 1 from chamber 13 to the by-pass is substantially closed due to the sealing action of piston 12 against the walls of cylinder 11. After piston 12 has assumed the described initial position, the gases above the piston in chamber 13 expand and force the piston downwardly. The gases in chamber 13 continue to expand and exert a force on the upper face of piston 12 until the upper face of the piston passes orifice 1. At this time, the gases in chamber 13 communicate with conduit 18 and the by-pass becomes operative around piston 12. The piston continues to travel, essentially by coasting, through the by-pass region between orifices 1 and 2 because of the momentum of the piston resulting from the force applied thereto as the piston began its downward stroke in chamber 13.

Because of the by-pass around piston 12, there is only a slight difference in pressure upon the upper and lower piston faces; the pressure at the upper face is slightly less than that of the lower face as piston 12 coasts downwardly through the region between orifices 1 and 2. In response to the pressure difference between the faces of piston 12 as the piston coasts downwardly through the central by-pass region, there is a flow of gas from chamber 14 through line 19, cold chamber 23, regenerator chamber 22, hot chamber 21 and conduit 18 into chamber 13. This heating of gas flowing upward through the by-pass increases the pneumatic pressure throughout the pump. Because of regenerator 22, which establishes a thermal gradient between hot chamber 21 and cold chamber 23, heat is applied to the gases flowing upwardly through the regenerator 22. Regenerator 22 enables the temperature of the gas flowing through the by-pass to increase before it is fed to heater chamber 21 and upper cylinder chamber 13. Since external heat is applied to gas already preheated by the regenerator, a higher peak gas temperature and pressure may be reached and efficiency of the pump is enhanced.

After the bottom face of piston 12 has moved downwardly past orifice 2, the by-pass is cut off and the bottom face of piston 12 compresses the gases in chamber 14 (including passageways 15) to reduce the piston velocity. The piston velocity is zero when minimum volume of chamber 14 is-reached. The gases in chamber 14, now being almost at maximum compression, begin to expand and drive piston 12 upwardly as a result of gaseous or pneumatic spring effect and a thermal lag effect caused by passageways 15. As piston 12 translates upwardly in response to the spring and thermal lag effect of the gases at the bottom of chamber 14 and before the bottom face of piston 12 passes orifice 2, gas being heated in the thermal lag passageways 15 and escaping from the thermal lag device through conduit 17 continues to expand in cylinder 11 to provide addi tional force to maintain piston 12 in an oscillating state. Passageways 15 provide a thermal lag, as described in my copending applications, and this increases the upward force on piston 12 to maintain the piston oscillation. The pressure in chamber 14 is augmented by the heated, expanding gases from passageways 15. By the time the bottom face of piston 12 is at the level of orilice 2 the pressure in chamber 14 has decreased almost to the same value as the pressure in chamber 14 during the downward stroke of piston 12 when it reached orifree 2.

As piston 12 moves upwardly so that its bottom face is above orifice 2, the by-pass is again unblocked and the pressures in chambers 13 and 14 both decrease in response to cooling of the gas therein. As piston 12 moves upwardly through the by-pass region, there is a slightly greater pressure on the upper piston face than on the lower face. Despite this pressure difference, piston 12 moves upwardly through the by-pass region in response to the momentum imparted thereto by the spring effect at the end of chamber 14 and the effects of the thermal lag created by passageways 15. The slightly higher pressure of gases in chamber 13 above the upper face of piston 12 relative to the pressure in chamber 14 at the time piston 12 coasts through the bypass region results in gas flow from chamber 13 to chamber 14 through conduit 18, heating chamber 21, regenerator chamber 22, cold chamber 23 and conduit 19. Thereby, heat in the gases flowing from chamber 13 through conduit 19 into chamber 14 is withdrawn from the gas by the regenerator and the cooling chamber 23 and pump pressure decreases. By using the regenerator a greater temperature differential is established between the hot and cold gases in chambers 13 and 14, which results in a greater pressure change during coasting of piston 12, to provide increased efficiency.

Gas continues to flow from chamber 13 to chamber 14 through the by-pass until the upper face of piston 12 passes orifice 1, at which time the by-pass is blocked and the pressure in chamber 13 increases with further upward movement of piston 12. The increased pressure in chamber 13 decreases the velocity of piston 12 until substantially maximum compression exists in chamber 13 at the top of the stroke of piston 12 at which time the piston velocity is zero. After maximum compression of the gases in chamber 13 is achieved, the gases in chamber 13, due to the pneumatic spring effect, begin to expand and drive piston 12 downwardly to repeat the cycle described.

Under the assumed conditions of conduit 26 being blocked, the pressures in chambers 13 and 14 versus position of the center of the piston are illustrated in FIG. 2. The arrows in FIG. 2 indicate the direction of piston movement, i.e., the downwardly directed arrows indicate the pressure in chambers 13 and 14 as piston 12 is moving downwardly, while the upwardly directed arrows indicate the pressures in the two chambers as the piston stroke is upward. The dashed lines and dots show the piston position in the cylinder and on a plot of pressure versus position. The pressure in chamber 13 as piston 12 moves in the region above the orifice of conduit 18 is defined by the line segments 31 and 32, while the pressure in the lower chamber 14 during this interval is defined by the line segments 33 and 34. While the lower face of piston 12 is below orifice 2, the lower chamber 14 pressure is indicated by line segments 35 and 36, while the upper chamber 13 pressure at this time is indicated by line segments 37 and 38. While piston 12 is coasting betweenthe by-pass in an upward direction, the pressures of upper chamber 13 and lower chamber 14 are given by segments 39 and 40. As piston 12 coasts in the by-pass in a downward direction the pressures in the lower chamber 14 and upper chamber 13 are indicated, by line segments 39 and 40, respectively.

It is noted from an inspection of FIG. 2 that there is a substantial change in pressure in chambers 13 and 14 while piston 12 is coasting through the bypass region. Under the assumed conditions of conduit 26 being blocked, this pressure change is maximized. If conduit 26 were unblocked and connected directly to the atmosphere, there would be almost no pressure change in chambers 13 and 14 as piston 12 coasts through the bypass region.

In both previously described conditions, substantially no work would be produced by the device. When an actual load is connected to conduit 26 the range of pressure in chamber 14 as piston 12 coasts in the by-pass region is less than when conduit 26 is sealed and greater than when conduit 26 is open to the atmosphere. In addition, the drop in pressure in chamber 14 occurs primarily in the early part of the upward coasting motion of piston 12, and the increase in pressure in chamber 14 occurs primarily in the early part of its downward coasting motion, according to the nature of the load. The resulting curve forms a clockwise type cycle. The pump can be designed to have a given thermopneumatic impedance. Matching the load to the pump is a factor in determining the power applied to the load by the pump.

Carnot efficiency of the device illustrated in FIG. 1 is approached because regenerator 22 is included in the by-pass, which allows a greater variation in temperature of the gas during the cyclic motion of piston 12 for a given rate of external heating and cooling. This re sults from applying heat to hot gases and removing heat from cooler gases to cause a greater temperature and pressure in the gases before the gases are fed to chamber 13 and a reduction of the temperature and pressure of the gas fed to chamber 14. The by-pass also enables a the center of oscillation of piston 12 to be determined approximately. In particular, if the two spring constants are equal, and there is no axial gravitational force, the piston 12 oscillates about a point; approximately midway between the orifices of conduits 18 and 19 into cylinder 11.

Those familiar with prior art, gaseous regenerative thermodynamic cyclic devices will appreciate that piston l2 performs the dual functions: of a displacer piston and a reversing piston, two distinct elements usually included in devices having regenerative cycles wherein the displacer piston is reversed in part pneumatically. In such prior art devices, the displacer piston functions during most or all of the cycle. Concurrently during at least a portion of the cycle, pressure changes across the reversing piston, which usually has at least one face in a chamber different from the chamber for the displacer piston, cause reversals in the direction of the displacer piston. In the oscillating piston pump of FIG. 1, however, piston 12 functions as a displacer piston while the by-pass is open and the same piston functions as a reversing piston when it moves beyond the coasting region into the region of cylinder 11 where pneumatic springs are formed by gases that cannot escape from the cylinder ends. Since the reversing chambers containing the pneumatic springs are merely extensions of the displacer cylinder, simplicity, reliability, and possibly efficiency, are greater than in prior art devices requiring structurally distinct reversing piston and a more complex reversing chamber and associated parts, accurate sealing surfaces, and thermal or frictional losses. In addition, the reversing process does not require an electric motor or depend on load pressure variations, as with such prior art devices, and the pump is essentially stall-free and operates at a frequency which is relatively independent of load.

Reference is now made to FIG. 3 of the drawing wherein there is illustrated a modification of the device illustrated in FIG. 1. In FIG. 3, a pair of cylinders 41 and 42, each respectively including free pistons 43 and 44, are interconnected with each other via conduit 45. Conduit 45 is provided with a T to which is connected conduit 46 that leads to passageways 47 which form a thermal lag heater responsive to heat generated by source 48. The thermal lag device comprising passageways 47 and heat source 48 simultaneously applies increased pressure to pistons 43 and 44 as the pistons are moving away from conduit 45 and thereby maintains the pistons in synchronized oscillation, whereby both pistons travel toward and away from conduit 45 simultaneously. Because of the synchronized, in-line motion of pistons 43 and 44 there is virtually no vibration or torque applied to the pump as a result of piston oscillation.

Cylinders 41 and 42 are provided with by-passes comprising heaters 51, regenerators 52 and coolers 53. The heaters, regenerators and coolers are formed by enlarging the walls of cylinders 41 and 42 in central regions thereof to form an annular space or passageways. Guide walls are provided in cylinders 41 and 42 to control the motion of pistons 43 and 44 to prevent possible entry of the piston into the chambers 51-53. Outside of the central region, pistons 43 and 44 are guided by the cylinder wall. Chambers 51-53 function effectively in the same manner as described supra with regard to chambers 21-23. Cold chambers 53 are in closest proximity to conduit 45 relative to regenerator and hot chambers 52 and 51. The hot chambers 51 are farthest from conduit 45, while regenerator chambers 52 are located intermediate of the hot and cold chambers.

A starter is provided in the system of FIG. 3 at the bottom of cylinder 42. The starter comprises a loose piston 55 that is translatable in cylinder 56 between stops 57 and 58 at the ends of the cylinder. Stop 57 is provided with an aperture to admit gas in cylinder 56 into cylinder 42. During normal operation, piston 55 is locked by a means (not shown) against stop 57 so that gas from cylinder 42 cannot escape into the starter housing and gas is not fed from the starter into the cylinder 42. In starting, loose piston 55 is oscillated back and forth to allow leakage of air from cylinder 42 through the passageway defined by the walls of piston 55 and cylinder 56 and provide a pressure impulse to piston 44. Oscillation of pistons 43 and 44 in a synchronized manner is quickly achieved by virtue of the thermal lag effects of passageways 47 and the cooling of gases by cold chambers 53. Other starter locations are also possible.

To enable useful work to be derived with the system of FIG. 3, conduits 59 and 60 are connected to orifices in the walls of cylinders 41 and 42 between conduit 45 and cooling chambers 53, preferably a point immediately adjacent cooling chambers 53. Conduits 59 and are connected to a common conduit 62, which in turn is connected to a load (not shown).

Reference is now made to FIG. 4 of the drawing wherein the system of FIG. 3 is modified whereby the near ends of cylinders 41 and 42 are provided with internal cooling fins, in the form of teeth 71 and the remote ends of the cylinders are provided with internal heating fins in the form of teeth 70, both of which sets of teeth have a relatively large surface area. Teeth are provided with resilient stops 72 at the bases thereof for easier starting. Teeth 71 mate with cooling teeth 73 carried by pistons 43 and 44. Teeth 70 mate with heating teeth 81 carried by the pistons. Teeth 81 opposite stops 72 may be truncated to reduce stress upon contact with the stop. The teeth at the top of cylinder 41 and the bottom of cylinder 42 can be heated by an external source while the teeth in the center of the pump assembly, at the bottom and top of cylinders 41 and 42, can be cooled by external sources.

In the pump of FIG. 4, cylinders 41 and 42 are connected together via a thermal lag device 74. Thermal lag device 74 is responsive to heat derived from source 75 and includes a number of heated passageways 76 which communicate with a common conduit that extends between orifices provided in cylinders 41 and 42 just above the crowns of teeth 71.

A by-pass structure, of the type described in conjunction with FIG. 1 or FIG. 3 is provided in each of cylinders 41 and 42 and is illustrated as comprising cold chamber 78, regenerator chamber 79 and hot chamber 80. Gas pumped by pistons 43 and 44 of FIG. 4 is fed to a common line 82 via conduits 83 and 84. Lines 83 and 84 are connected to cylinders 41 and 42 through orifices positioned on the cylinder wall at approximately the same vertical location as the orifices to conduits leading between cold chambers 78 and cylinders 41 and 42. Thereby, gas is simultaneously fed by lines 83 and 84 in synchronism to common conduit 82 as pistons 43 and 44 approach conduits 83 and 84 in their travel towards the center of the piston assembly.

An exemplary load driven by the gases flowing to conduit 82 will now be described as comprising high pressure gas storage chamber 85 and low pressure gas storage chamber 86. Conduit 82 is connected to high pressure chamber 85 via check valve 87, while the low pressure chamber 86 is connected to conduit 82 via check valve 88. Check valve 87 prevents the flow of gas from high pressure chamber 85 to conduit 82. While pistons 43 and 44 have unblocked conduits 83 and 84 in their travel away from the center of the piston assembly, gas from low pressure source 86 is sucked through check valve 88 and conduit 82 into cylinders 41 and 42. During the portion of the cycle while conduits 83 and 84 are not blocked by pistons 43 and 44 and the pistons are moving towards the center of the pump assembly, compressed gas is fed to conduits 83 and 84 and fed through check valve 87 to high pressure chamber 85. Compressed gas flowing in conduit 82 at this time is not fed to low pressure chamber 86 because of check valve 88. High pressure and low pressure chambers 85 and 86 are connected to the inlet and outlet of an appropriate load 89, which may comprise a heart pump or other pneumatic device driven by a relatively constant pressure differential.

Reference is now made to FIG. 5 of the drawing wherein there is illustrated a modification of the embodiment illustrated by FIG. 4. In FIG. 5, upper and lower cylinders 91 and 92 in which free pistons 93 and 94 oscillate in synchronism are provided with internal heating and cooling fins (not shown) and external heating sources 48 and cooling sources 49. The external heating sources are located at the upper and lower ends of cylinders 91 and 92, respectively, while the external cooling means are provided at the lower and upper ends of cylinders 91 and 92, respectively. Some thermal lag effect may be obtained from the internal fins, thereby helping to drive the pistons. The cooler ends of cylinders 91 and 92 are connected together via conduit 45 which is connected to thermal lag device 47 in the same manner indicated supra, in FIG. 3. A by-pass is provided in cylinders 91 and 92 at the same places as indicated supra regarding FIG. 1. The by-passes 95 and 96 for cylinders 91 and 92 include only regenerating chambers 95 and 96 and appropriately located conduits. The heating and cooling chambers of the previously discussed embodiments are incorporated directly in cylinders 91 and 92 and comprise the heating and cooling sources referred to above.

In the embodiment of FIG. 5, hot, rather than cool, gases are the pumped gases. To this end, conduits 97 and 98 are respectively provided with outlets connected to orifices in cylinders 91 and 92. The outlets of conduits 97 and 98 are respectively connected to the heated upper and lower segments of cylinders 91 and 92, at a position approximately aligned with the outlets of regenerators 95 and 96 into the heatedportions of the cylinders. I-Iot gas may be pumped in other embodiments also.

In FIG. there is illustrated another type of device for feeding a load in response to oscillatory gases fed by conduits 97 and 98 to a common outlet conduit 99. The load driving device comprises check valve 101 poled in a direction to feed low pressure gas into conduit 99 and prevent the flow of high pressure gas from conduit 99 through it. A flow limiter 102 is connected in series with a further check valve 103, poled in such a manner as to pass high pressure gas from the pump to a load. Thereby, regulation is provided as to the flow of gas from the pump into a chamber or other region of space.

Reference is now made to FIG. 6 of the drawing wherein is illustrated a modified two piston system.

In the embodiment of FIG. 6, pressure pulses are fed to a piston from a pressurized fluid source to maintain the piston in oscillation. The source may be pressurized by a feedback arrangement from the load. The pressure pulse arrangement replaces the passageways in the previously discussed embodiments in which the pressure effect of thermal lag was used to sustain oscillation.

In FIG. 6, load 204 is driven by outlet conduits 105 and 106 via conduit 107. Conduits 105 and 106 are re spectively connected to orifices at the top and bottom of cylinders 108 and 109. The orifices leading to conduits 105 and 106 are approximately in alignment with orifices leading from cold chambers 111 of by-pass devices of the type described with regard to FIG. 1. The bottom and top of cylinders 108 and 109 are connected via conduits 113 and 114, which extend into the cylinders by an amount necessary to establish stops for free oscillating pistons 115 and 116. Conduits 113 and 114 are connected via a T to conduit 217 that is in turn connected to high pressure gas source 104 via solenoid controlled valve 117. Solenoid controlled valve 117 is normally closed, and is actuated to an open condition for a relatively short predetermined length of time in response to a pulse fed thereto by electrical network 1 18. Electrical network 118 is responsive to signals derived by proximity sensors 119 and 120 at the bottom and top of cylinders 108 and 109, respectively. Sensors 119 and 120 may be of any conventional type, e.g., capacitive, that derive output signals indicative of displacement between the pistons and sensors.

The electrical circuit includes a pair of differentiators, each responsive to one of sensors 119 and 120. The differentiators derive output pulses when pistons 115 and 1 16 come closest to the proximate ends of cylinders 108 and 109 and begin moving away from the ends of the cylinders.

If pistons 115 and 116 are perfectly synchronized, the output signals of the two differentiators occur simultaneously and are combined to derive an electrical pulse. The pulse is fed to valve 117 to open the valve momentarily to enable a pressure pulse to be fed from chamber 104 through conduits I13 and 114 to maintain pistons 115 and 116 in oscillation. The pressure pulse occurs at a time while pistons 115 and 116 are both moving away from the bottom and top of cylinders I08 and 109 by virtue of the gas springs at the cylinder ends. The pressure pulse is timed to add drive force to the pistons in such a manner that synchronized oscillation is sustained in response thereto.

If pistons 115 and 116 are not perfectly synchronized, the instants of maximum proximity sensed by sensors 119 and 120 do not occur simultaneously. Circuit 118 is provided with a means e.g., an AND gate responsive to signals from the differentiators indicating both pistons are moving away from sensors 119 and 120, for enabling only the last occurring pulse derived by the differentiators to be utilized to open valve 117. The pressure pulse fed by valve 117 to line 217 has a greater effect on the lagging piston. This is because the lagging piston is in a smaller volume than the faster piston and velocity of the slower piston is less than the faster piston, to provide higher fluid pressure for the pulse. The pressure pulse fed by line 217 to conduits 113 and 114 can be heated by feeding the conduit 217 through apertures provided in a regenerator 123 and heater 1 12 so that it supplies added energy to the piston and higher efficiency is attained.

Chamber 104 is pressurized by gas fed back from or diverted from load 204 while piston 116 is coasting downwardly in the cylinder 109, i.e., during the power stroke of piston 116. The gas fed back from the load is fed through check valve 124, poled in such a manner as to permit gas to flow from conduits and 106 into chamber 104, but not vice versa. Since the maximum pressure of the hot ends of cylinders 108 and 109 is typically less, during pneumatic spring action, than the pressure in storage chamber 104, while the maximum spring pressure in the cold ends would be greater than pressure in chamber 104, the hot cylinder ends are made common and used for synchronizing rather than utilizing the cold cylinder ends for this purpose as was illustrated previously in the embodiments of FIGS. 3-5.

In the embodiment of FIG. 6, there may be greater efficiency than in the previously described embodiments because of the more efficient structure utilized for feeding added energy to the pistons to maintain them in an oscillatory state. Greater efficiency may re sult since the pressure in chamber 104 is developed from the regenerative gas cycle, i.e., feeding gas through regenerators 123 instead of from a thermal lag type heater. The system of FIG. 6 has particular advantage with devices having greater power output than the previously described systems, where greater thermodynamic efficiency is required and the additional moving parts required to attain the added efficiency do not detract from overall performance of the device.

Reference is now made to FIG. 7 wherein the pump of FIG. 6 is modified to eliminate the requirement for an electrical network and a pneumatic device is employed to control the pulses of pressurized gas which maintain pistons 131 and 132 in synchronous oscillation in cylinders 133 and 134. Pressure pulses from storage chamber 104 are periodically applied, once during each cycle of oscillation of the slowest one of pistons 131 or 132, to the bottom and top of cylinders 133 and 134 via flow limiter 135, series connected spring loaded cup shaped valves 136 and 137, and conduits 138, 139 and 140. Valves 136 and 137 are located at sealed ends of tubes 141 and 142, the other ends of which extend into the bottom and top of cylinders 133 and 134 to form stops for pistons 131 and 132 for easier starting of the device. Pistons 131 and 132 are provided with cylindrical appendages 144 and 145 which, during a small portion of the cycle, extend into tubes 141 and 142. Valves 136 and 137 are pulled against the closed ends of tubes 141 and 142 by virure of the spring tension and normally closed orifices in tubes 141 and 142 leading to conduits 138, 139 and 140. To open valves 136 and 137 in response to movement of pistons 131 and 132, tubes 141 and 142 are connected to the ends of cylinders 133 and 134 via check valves 146 and 147. Orifices in tubes 141 and 142 that communicate with check valves 146 and 147 are positioned so that they are near valves 136 and 137 but are not blocked while valves 136 and 137 are closed.

In operation, valves 136 and 137 are normally closed. As appendages 144 and 145 enter tubes 141 and 142, they compress gases in the tubes to a greater extent than the gases at the bottom and top of cylinders 133 and 134. Thereby, valves 146 and 147 open, tending to equalize the pressures in tube 141 and cylinder 133, as well as the pressures in tube 142 and cylinder 134. Due to the pressure in tubes 141 and 142 as well as cylinders 133 and 134, the velocity of pistons 131 and 132 drops to zero and, due to the gaseous spring effects, the pistons begin thereafter to move away from the central portion of the assembly. In response to movement of pistons 131 and 132 away from the central portion of the assembly and while appendages 144 and 145 are in tubes 141 and 142, the pressure in tubes 141 and 142 is reduced and a suction force is exerted on valves 136 and 137 to open the valves and allow gas to flow through them. Valves 136 and 137 stay open until appendages 144 and 145 are withdrawn from tubes 141 and 142, at which time gases from cylinders 133 and 134 flow into tubes 141 and 142 and valves 136 and 137 are closed, because of their spring tension.

If pistons 131 and 132 are synchronized, valves 136 and 137 open and close simultaneously. In response to valves 136 and 137 both being open, gas flows from pressurized chamber 104 through flow limitor 135, conduits 138-140, and valves 136 and 137 to cylinders 133 and 134. The response of valves 136 and 137 only to suction and the resulting gas flow are such that gas is not delivered into cylinders 133 and 134 by conduit 140 until both pistons 101 and 132 have begun to move away from the center of the assembly. Thereby, the gas flow assists the gaseous spring effect to sustain oscillation. Gas continues to flow through conduit into cylinders 133 and 134 until one of appendages 144 and is out of tube 141 or 142. Pistons 131 and 132 cannot be overdriven, despite the relatively long time interval during which drive pressure is applied to them by conduit 140 by proper overall design.

If pistons 131 and 132 are out of synchronism, whereby one piston begins to move away from the center of the assembly before the other, gas does not flow into cylinders 133 and 134 via conduit 140 until the lagging piston has begun to move away from the center. Gas flow is prevented until this time because of the series connection of valves 136 and 137. The gas flow into cylinders 133 and 134 has the greatest effect on the lagging piston because of the lower velocity of the lagging piston, and the lesser volume between the end of the cylinder nearest conduit 140 and the closer face of the lagging piston contributes to a slower flow rate of gas into this lagging chamber than the leading chamber. Therefore, a pressure differential along the conduit 140 results in a greater pressure in the lagging chamber than the leading chamber, so that the lagging piston receives a pneumatic impulse, which is relatively greater as well as earlier in its cycle, thereby tending to maintain synchronism.

Reference is now made to FIG. 8 of the drawing wherein there is illustrated an oscillatory gas pump 311 which feeds oscillatory pressure variations to power converting alternator 312, which in turn supplies alternating electric current to an electric load 313. Separate consideration will be given to pump 311 and alternator 312, both of which are free oscillating piston devices.

Pump 31 1 includes a pair of sealed cylinders 314 and 315, each respectively including free pistons 316 and 317. The ends of cylinders 314 and 315 in closest proximity to each other are interconnected with each other via conduit 318. Conduit 318 includes a T connection, to which is connected conduit 319 that leads to a thermal lag device comprising passageways 320 and heat source 321. The thermal lag device applies increased pressure to pistons 316 and 317 as the pistons are moving simultaneously away from conduit 318. Thereby, pistons 316 and 317 are operated synchronously so there is virtually no vibration or torque applied to pump 311 as a result of piston oscillation.

Cylinders 314 and 315 are respectively provided with variable length by-passes 323 and 324. In each of bypasses 323 and 324 there is included in seriatim a heating chamber, a regenerator chamber, and a cooling chamber. Cooling chambers 325 and 326 are located in by-passes 323 and 324, respectively, at the ends of the by-passes closest to conduit 318, while heating chambers 327 and 328 are located in the by-passes at the ends of the by-passes closest to the ends of cylinders 314 and 315 most remote from conduit 318. In bypass 323, between cooling chamber 325 and heating chamber 327, is regenerator chamber 329, while regenerator chamber 331 is located in by-pass 324 between cooling chamber 326 and heating chamber 328.

To control the lengths of by-passes 323 and 324, the ends of the by-passes closest to conduit 318 are connected through multiport valves 332 and 333 to the cylinder walls near the ends of cylinders 314 and 315 closest to conduit 318. Valves 332 and 333 include ports 334 and 335 respectively connected to cold chambers 325 and 326. Valve 332 includes five additional ports 336-340 having connections to cylinder 314 at different locations along thelength of the cylinder. The distance between port3336 and the other end of by-pass 323, the end connecting hot chamber 327 to cylinder 314 is great enough to position the center of piston oscillation and to provide the minimum desired pumping power. During normal operation this distance is equal to or greater than the length of piston 316 to enable piston 316 to coast through a portion of the cylinder bypass region. In certain instances, however, the distance between port 336 and the other end of by-pass 323 may be less than the length of piston 316, if it is desired to minimize coupling of pressure variations from pump 311 to alternator 312. Valve 332 is constructed so that a flow path is established from inlet port 334 to only one or two of ports 336-340 at a time, whereby adjustment of valve 332 effectively changes the length and position of by-pass 323. Changing the length of by-pass 323 alters the magnitude and time duration of the pressure variations supplied by pump 311 to alternator 312, thereby to modulate the amount of voltage or power supplied by the alternator to load 313.

Valve 333 controls the length of by-pass 324 for cylinder 315 in exactly the same manner that valve 332 controls the length of by-pass 323 for cylinder 314. To enable pistons 316 and 317 to be maintained in synchronism and approximately the same amount of gas pressure to be supplied by each of cylinders 314 and 315 to alternator 312, valves 332 and 333 are generally adjusted in a like manner so that the lengths of bypasses 323 and 324 are always substantially the same.

Oscillatory pressure variations from cylinders 314 and 315 are supplied to alternator 312 via multiport valves 342 and 343, having ports connected to alternator 312 via conduits 344, 345 and 346. Multiport valves 342 and 343 are identical with valves 332 and 333 and include five ports having connections to different positions along the length of cylinders 314 and 315 opposite from the inlet ports to valves 332 and 333 from the cylinder walls. The positions of valves 342 and 343 are generally controlled in synchronism with those of valves 332 and 333 so that gas communicates through corresponding ports to the cylinders; thus, in general, all of the valves simultaneously have connections to cylinders 314 and 315 through the ports equidistant from conduit 318. By synchronizing the positions of valves 332, 333, 342 and 343 gas is efficiently trans ferred from the ends of cylinders 314 and 315 proximate conduit 318 to alternator 312 since the conduits leading to the alternator are opened and closed at the same time as the by-pass. To enable the oscillatory pressure variations derived from cylinders 314 and 315 to be applied in synchronism to alternator 312, the lengths of the flow paths through valves 342 and 343 and conduits 345 and 346 are maintained substantially the same. In theory, however, an alternator or other load may be connected to any portion of the pump.

The alternator 312 and conduits 344, 345 and 346 may be cooled to improve the efficiency of the alternator and pump. In an alternative embodiment, not shown, the valves 342 and 343 may be eliminated, and the conduits 345 and 346 connected directly to the conduits which connect cold chambers 325 and 326 to ports 334 and 335 in valves 332 and 333. As an additional alternative, the axial location of the hot end of the by-pass region may be varied by means of a valve and porting arrangement. The axial location of the hot end may be varied simultaneously with, or instead of, the valve and porting arrangement at the cool end of the by-pass. Further, the pump inlet/outlet may be connected to the hot, rather thancool, end of the by-pass region, for pumping hot gas. Also, by combining certain functions, some of the duplication inherent in the two by-passes, and the two load connections, may be eliminated, e.g., the functions of valves 332 and 333 may be performed by a single valve, or the heating, cooling, or regenerator chambers and/or by-passes may be combined.

To prevent pistons 316 and 317 from contacting end faces of cylinders 314 and 315, and for easier starting, the cylinder end faces are provided with resilient stops 356-359. Stops 356-359 are normally inoperative during a typical oscillatory cycle of pistons 316 and 317 since the pistons are prevented from reaching the ends of cylinders 314 and 315 by pneumatic springs caused by gases in the cylinders.

After starting, pistons 316 and 317 are driven in synchronism, so that both approach conduit 318 at approximately the same time and both recede from the conduit simultaneously. Thereby, gas is supplied by cylinders 314 and 315 to conduits 345 and 346 at substantially equal rates. These in-phase gas flows are com bined in conduit 344.

The thermally induced change in the pressure of gases in chambers 361 and 363 while piston 316 is coasting in the by-pass region essentially provides the pumping power. The pressure change during each cycle is dependent upon the amount of gas heated and cooled in the by-pass and therefore upon the length of the by-passed region of the cylinder. In particular, if the length of by-pass 323 is a minimum, whereby port 336 is connected through valve 332 to orifice 334, the pump output power is a minimum, and may be substantially zero if there is no coasting of piston 316. The pressure variations in chambers 361 and 363, and therefore the pump output power available, are maximized when the length of by-pass 323 is greatest, as occurs by connecting port 340 through valve 332 to orifree 334. The pressure changes in chambers 361 and 363 are dependent upon the amount of heating and cooling of the gas in the by-pass, and therefore the length of the coasting region. The fraction of the cycle during which pneumatic power is applied to a load also increases with the length of the by-pass, and this contributes to the increase in output power when the coasting region is lengthened by means of the valves 332 and 342. Power and frequency are also affected by a change in mean position of the by-pass, partly due to its effect on average gas temperature and therefore pressure. Independent control of by-pass length and position can be used to obtain independent control of power and frequency. In particular, when the length of by-pass 323 and therefore the piston coasting region is minimized, whereby piston 316 blocks the flow of gas from chamber 363 to valve 342 for a relatively long time interval during each oscillatory piston cycle, pressure variations are coupled from chamber 363 through valve 342 to conduit 345 for only a. relatively short time interval. In contrast, when valves 332 and 342 are arranged so that the by-pass length is maximized, pressure is supplied from chamber 363 to conduit 345 for a relatively long time interval.

In general, in order to reduce susceptibility to stalling, the dimensions of the various pump embodiments are such the piston never completely traverses a load port during rebounding. Thus, in FIG. 8, the upper face of piston 316 never goes below the load port selected by valve 342, except for special applications. This decoupling of the load from the device during this piston rebound reduces susceptibility of the free piston pump to stalling (in addition to balancing of the load pressures on the two piston faces during coasting).

The oscillatory pressure variations derived by free piston pump 311 are coupled to alternator 312 through conduit 344. Alternator 312 includes a pair of high magnetic permeability (e.g., ferromagnetic) free pistons 371 and 372, respectively located in cylinders 373 and 374. Cylinders 373 and 374 are connected by conduits 375 and 376 to conduit 344 so that the periodic pressure variations in conduit 344 tend to produce syn chronous oscillation of pistons 371 and 372.

Pistons 371 and 372 are part of magnetic circuits 377 and 378, respectively. Magnetic circuits 377 and 378 include ring shaped permanent magnets 379 and 380, having pole faces fixedly positioned along the length of cylinders 373 and 374. Positioned in a hollow central portion of magnets 379 and 380 are circularly wound coils 382 and 383 in which are developed a.c. voltages in response to the oscillatory motion of pistons 371 and 372 varying the flux in the magnetic circuits in an oscillatory manner. To prevent magnetic short circuits between the poles of magnets 379 and 380, pistons 371 and 372 are provided with ring-like cutout segments in which are mounted rings 384 and 385 of substantially nonmagnetic material. To provide good efficiency in generating a.c. voltages in coils 382 and 383, the lengths of rings 384 and 385 along the axis of cylinders 373 and 374 are approximately equal to the minimum distance between the north and south poles of the magnets.

To enable the center of oscillation of pistons 371 and 372 to be fixed, by-pass regions are provided in cylinders 373 and 374. The by-passes may have a length equal to, greater than or less than the length of pistons 371 and 372. The by-passes may take the form of a passage external to cylinders 373 and 374, as disclosed in conjunction with by-passes 323 and 324, or they may be wholly within the cylinders, as described in my copending application, Ser. No. 121,371.

In the specific embodiment illustrated in FIG. 8, the by-pass of cylinder 373 is provided by axial grooves 386 in the cylinder wall portion surrounded by coil 382. Axial grooves 387 in the sides of piston 371 near its ends shorten the effective, or sealing length of the piston. Grooves 387 are long enough to allow gas flow in the by-pass sufficient to maintain piston position under conditions of variable system pressure or other forces on the piston, but do not extend over the entire length of the piston in order to maintain a reasonably good seal between the circumference of piston 371 and the walls of cylinder 373 beyond the by-pass.

In response to synchronized, oscillatory motion of free pistons 371 and 372 resulting from the periodic pressure variations in conduit 344 and the pneumatic springs at the remote ends of cylinders 373 and 374,

currents of like phase are induced in coils 382 and 383. The voltages generated in coils 382 and 383 can be supplied to separate loads, or can be supplied to the same load 313 in an additive manner.

Linear alternator magnetic circuit designs other than that of magnetic circuits 377 and 378 can be employed in alternator 312. If desired for certain designs, oscillation of the alternator free pistons can extend outside of the by-pass region. The extent of travel of the free pistons in general depends on the load, the design of the pistons, cylinders and by-passes, as well as the amplitude of pressure variations supplied to the alternator by the external pressure source, pump 312.

To prevent damage to cylinders 373 and 374 and pistons 371 and 372 and for easier starting, the cylinders are provided with resilient stops 391-394 on their top and bottom faces. Normally, pistons 371 and 372 do not engage the stops, which are provided primarily as a safety means and for easier starting.

While free piston pump 311 is shown as a source for feeding oscillatory pressure pulses into conduit 344, it is to be understood that other oscillatory pressure sources can be employed.

In many instances, it is necessary to modulate the amount of power derived from alternator 312, which functions as a pneumatic to electric power converter. Changes in the amplitude and frequency of pressure variations fed to alternator 312 via conduit 344, cause the length of the stroke and frequency of pistons 371 and 372 to be varied. In accordance with another aspect of the present invention, the pressure variation amplitudes in conduit 344 are controlled in response to changes in load 313. To this end, the power supplied to load 313 by coils 382 and 383 is monitored by any suitable means (not shown), such as voltage and frequency comparators. If the voltage across load 313 is above or below a predetermined value necessary to power the load, the amount of power derived from the pump 311 is varied by controlling the length and/or position of bypasses 323 and 324 for cylinders 314 and 315. The lengths of the by-passes are varied by controlling the positions of valves 332 and 333, 342 and 343, which are preferably ganged together by mechanical connection 395. Mechanical connection 395 can be responsive to an operator manually monitoring the voltage or aservo mechanism can be provided that is responsive to the deviation between the load voltage and a target value therefor and automatically operates the valves. Similarly, frequency may be simultaneously controlled.

In response to changes in the load, the lengths of bypasses 323 and 324, or in gas average temperature, there may be a tendency for the frequency of oscillation of pistons 316, 317, 371 and 372 to change. The effect on frequency of a change in by-pass length is compensated to some degree by the fact that a change in pump pressure differential increases the pneumatic spring constant at one end of the cylinder and decreases the pneumatic spring constant at the other end of the cylinder. In addition, the change in coasting time is compensated to a degree by the change in cold pneumatic spring constant in chamber 363 resulting from the change in volume of the cold reversing chamber when the by-pass length is altered.

In certain instances, however, changes in the average temperature and therefore pressure of gas in the system resulting from changes in the mean position of bypasses 323 and 324 when the lengths of these by-passes are varied may materially change the frequency of oscillation of the pistons. To enable the frequency of oscillation to be maintained constant despite changes in load, thermal input, by-pass length, or other factors,

the by-pass mean position may be varied independently of bypass length to control the average pressure of working gas and the values of pneumatic spring constants. By-pass position and length may be controlled independently by using a multiport valve at the hot end of each by-pass in addition to valves 332 and 333.

Freqeuncy may also be varied in the embodiment of FIG. 8 by changing tlie gas volume of conduit 344 and therefore the density of working gas and values of the spring constants. To this end, there is provided a bellows 396 which is connected to an intersection between conduits 344, 375 and 376. Bellows 396 is mechani cally driven by rack and pinion 397 and 398, the former being fixedly connected to one face of the bellows. Pinion 398 is driven by comparing a characteristic(s) of load 313, e.g., the frequency and/or voltage across load 313, as derived by a suitable meter(s) (not shown) with a predetermined value therefor. In response to the load characteristic(s) differing from the predetermined value, pinion 398 is driven by a manual control or in response to a signal automatically derived from a servo mechanism responsive to a comparison of the load frequency and desired frequency. Changes in average pressure within pump 311 and alternator 312 also affect the amount of power derived from the pump and alternator. Conversely, changes in by-pass length affect the frequency of the pump and alternator. By using a dual feedback arrangement the frequency and voltage supplied to the load by the pump alternator combination can be maintained relatively constant under variable load conditions. It is also possible, in order to lessen the temporary displacements of the centers of oscillation of the alternator pistons as a result of a rapid change in system pressure, to operate simultaneously three bellows, rather than one, for correcting voltage and frequency. The second and third bellows would be relatively small and be connected to the top and bottom of cylinders 373 and 374. Thus, average system pressure can be changed approximately equally on both sides of each alternator piston, to help maintain their centers of oscillation during conditions of variable load, and decrease the required lengths of alternator cylinder by-passes. Further, under certain conditions, control of the position of one or both ends of the bypass in the pump, as well as heat exchanger temperatures, can be employed to maintain proper voltage and frequency under conditions of variable load, without use of a bellows. Alternatively, the use of bellows or other means of varying system pressure, coupled with control of the heat exchanger temperatures, may be sufficient for controlling frequency and voltage without varying the length and position of the pump by-passes. In addition, performance may be controlled by varying the rebound chamber volumes by means of adjustable pistons or bellows at the ends of the cylinders, thereby affecting penumatic spring constants as well as overall pressure in the system. Also, the impedance of the pneumatic connection between the pump and alternator can be controlled, as by means of a valve, to vary the power and frequency. Or, means of varying the heater, regenerator, and/or cooler capacities in the bypass can be used to vary power. Still other means for controlling pump output power and frequency are described below. The variable by-pass length has good heat economy at low, as well as high, power levels, and its stored thermal energy is avialable for rapid power increase, but this control technique is more complex than those described below.

An alternative method of starting the pump driven alternator 312 is to apply electrical power, of proper waveshape, to the alternator so that its pistons will start those of the pump.

In certain instances, an oscillating free piston pump has an inlet and outlet which are partially or completely separate from each other, and is used to pump gases from one point to another, as illustrated in FIG. 9. In FIG. 9, a free piston pump 401 includes a single cylinder 402 through which free piston 403 is translated in an oscillatory manner in response to pressure applied to the piston by thermal lag device 404, located at one end of cylinder 402. Variable length by-pass 405, including hot chamber 406, regenerator chamber 407, and cold chamber 408, is provided around piston 403. An orifice at the bottom of chamber 408 is connected through valve 409 to one of orifices 41l415 spaced at different points along the length of cylinder 402. Disposed in approximate alignment with orifices 411-415 are five orifices in the cylinder wall connected to valve 416 which includes an output orifice 417 that is connected to a suitable load. Preferably, orifice 417 is connected to the load through check valve 418. Altematively, valve 416 may be eliminated and orifice 417 connected directly to conduit 423, or to any portion of the cylinder wall.

In the embodiment of FIG. 9, gas is drawn into cylin' der 402 from source 419. Gas from source 419 is fed through cold chamber 421 and check valve 422 to conduit 423, which is also connected to cold chamber 408 and valve 409. Gas is supplied to conduit 423 from source 419, after having been cooled in chamber 421, during the portion of the oscillatory cycle of piston 403 when the pressure in conduit 423 is less than the pressure of source 419, Le, primarily when piston 403 is travelling upwardly in the by-pass region. Thereby, cold gas from chamber 421 mixes with cold gas flowing from chamber 408 into conduit 423 and the mixture is fed into the portion of cylinder 402 below the lower face of piston 403. When piston 403 is coasting in a downward direction in the by-pass region of cylinder 402 the pressure in conduit 423 becomes greater than the pressure of source 419, whereby check valve 422 is closed. By feeding cold, and therefore dense, gas from source 419 and cold chamber 421 into cylinder 402 through conduit 423 while piston 403 is coasting upwardly in the by-pass region, the amount of gas drawn into the cylinder for pumping, and the differential temperature of gases in the cylinder over a cycle are increased, to increase the efficiency of the pump.

Check valve 418 supplies gas from cylinder 402 to a load primarily while piston 403 is coasting in a downward direction through the by-pass region of cylinder 402. With piston 403 coasting in cylinder 402, the pressure of the gas supplied through valve 416 to the check valve 418 generally becomes greater than the load pressure, and only then is the load responsive to the pressurized gas in the portion of cylinder 402 below the lower face of piston 403 because check valve 418 otherwise is closed by the higher pressure of the load. Alternatively, the pump outlet may be located near the top end of cylinder 402 for pumping hot gases.

The arrangement of FIG. 9 can be adopted to a synchronized, two free piston arrangement, as illustrated in FIG. 10. The pump of FIG. is essentially the same as pump 31 1 of FIG. 8, except that gas from an external source 424 is fed through cold chamber 421 and check valve 422 to conduits 427 and 428, which preferably are of equal length to connect the output orifice of the check valve 422 to orifices of regenerators 429 and 430. Regenerators 429 and 430 are connected in by passes 431 and 432 for cylinders 433 and 434. Bypasses 431 and 432 respectively include heating chambers 435 and 436 which are connected to the top and bottom portions of cylinders 433 and 434. The bypasses 431 and 432 are completed through variable position valves 437 and 438, the functions of which may alternatively be performed by a single valve.

It is to be noted that check valve 422 is connected directly to regenerators 429 and 430, without being connected to a cooling chamber in the by-pass. In many instances, the increased efficiency attained through the use of cooling chamber 421 obviates the requirement of cooling chambers in the by-passes 431 and 432. In certain systems, regenerators 429 and 430 can be eliminated because of the inherent heat storage properties of conduits 427 and 428. Similarly, in FIG. 9, it is possible in certain instances to connect an orifice of hot chamber 406 directly to conduit 423, thereby eliminating regenerator 407 and cold chamber 408. In the alternative, it is possible in the system of FIG. 9 to eliminate cold chamber 408. If a source of hot gas is available for pumping, the need for heating chambers in the bypasses of the pumps in FIGS. 9 and 10 may similarly be obviated.

Pressure variations in cylinders 433 and 434 are supplied to separate loads via output ports 439 and 440 and check valves 470 and 471, or the ports may be connected to a common load via a T connection (not shown) so that in phase flows from cylinders 433 and 434 are combined. Ports 439 and 440 are positioned in the hot ends of cylinders 433 and 434 in axial alignment with ports from the hot ends of the cylinders to by-passes 431 and 432. In the alternative, multiple output ports can be provided in the cold ends of cylinders 433 and 434, as illustrated in FIGS. 8 and 9.

In accordance with a further embodiment of the invention, illustrated in FIG. 11, the thermal lag heater comprises blind passageways 441 located in free piston 422. Passageways 441 extend longitudinally in piston 442 from the face of the piston positioned to be responsive to cold gas flowing into lower chamber 443 of cylinder 444 from by-pass 445 and from a load connected to cylinder port 458. Passageways 441 extend through the length of piston 442 for a distance sufiicient to provide adequate temperature and volume of the thermal lag chamber.

Preferably, in normal operation piston 442 is indirectly heated so that no additional heat source is required for the thermal lag device. To this end, the upper face of piston 442 forming an end wall of upper chamber 446 of cylinder 444 is heated by hot gas flowing out of by-pass 445 into upper cylinder chamber 446 via port 447. The piston is also heated by the hot cylinder wall surfaces. Heat from the upper piston face is conducted through the piston to the walls of passageways 441 to heat cold gas fed into the bottom chamber 443 and thence into the passageways from by-pass 445 as the piston travels downwardly past bottom port 459 that connects the by-pass to cylinder 444. The cold gas flows into passageways 441, is heated therein and expands to flow out of the passageways as piston 442 begins its upward travel, thereby sustaining oscillation of the free piston.

Stops in chambers 443 and 446 are formed by compression spring means 448 and 449 fixedly mounted to extend longitudinally from the lower end face of piston 442 and the upper end face of cylinder 444. Spring means 448 is a single compression spring fixedly mounted in short passageways 451 of piston 444. Spring means 448 is preferably mounted on the piston, rather than the bottom end face of cylinder 444, to maintain it at a higher temperature and to use the thermal lag effect from its hot surfaces and those of its mounting passageways to help sustain piston oscillation.

Spring means 449 comprises several metal compression springs positioned on the upper face of cylinder 444 to form thermal lag passageways for helping to sustain piston oscillation. To this end spring means 449 may comprise plural coaxial springs having different diameters or plural springs having different axes relative to the upper end face of cylinder 444. Preferably springs 449 are indirectly heated by hot gas flowing from by-pass 445 and by radiant heating. The thermal lag device formed by the passageways of spring means 449 may also cool some of the hot gas in the cylinder as piston 442 is rebounding from the lower end face of cylinder 444. Cooling of the hot gas during this period tends to decrease the pressure of the gas upon the upper piston face to assist in sustaining oscillation of piston 442. While spring means 449 is preferably indirectly heated, it is to be understood, however, that spring means 449, or other thermal lag means opening into the top of cylinder 444, can be directly heated if necessary.

The structure of FIG. 11 can be incorporated in a device having two or more synchronized pistons by providing a cylinder for each piston and by connecting one chamber of each cylinder together. Preferably, chambers having the same configurations are interconnected and greater synchronization can be attained by interconnecting the chambers providing the greatest thermal lag forces. In some instances, however, to achieve synchronization, it may be necessary to utilize a common thermal lag chamber that is connected to one chamber of each cylinder. The single directly heated chamber could be employed in combination with separate thermal lag devices for each cylinder. For example, the directly heated thermal lag device of FIG. 8 could be provided between a pair of cylinders including free pistons and thermal lag springs illustrated in FIG. 11.

The by-pass 445 illustrated in FIG. 11 is of a form which, although functionally similar, is structurally different from that suggested in the other embodiments. In particular, by-pass 445 includes concentric chambers 452, 453 and 454 forming the hot, regenerator and cold chambers. Inner, hot chamber 452 surrounds centrally located heater 455, while outer, cold chamber 454 includes cooling fins 456 on its exterior surface. Gas flows axially and/or radially within chambers 452454, through passageways in the chambers. Gas 

1. An oscillating piston apparatus comprising a cylinder, a free piston in said cylinder dividing the cylinder into first and second variable volumes, means for sustaining oscillation of the piston in the cylinder, a by-pass between the first and second volumes such that the piston coasts through a region of the cylinder between ends of the cylinder, a regenerator means in the by-pass, means for restricting the by-pass during the piston oscillation while at least one volume has a value in a minimum range, means for feeding cool fluid into the second volume, and means for feeding hot fluid into the first volume.
 2. The apparatus of claim 1 wherein the by-pass includes a port in a side wall of the cylinder, said port being blocked by the piston while one of the volumes is in the minimum range to form the restricting means and said port being unblocked while the piston is coasting through the region.
 3. The apparatus of claim 1 further including means for feeding fluid from one of said volumes to a load as the piston coasts through the region.
 4. The apparatus of claim 1 wherein the means for sustaining oscillation comprises thermal lag means having an inlet communicating with one of the volumes while the one volume has values in a minimum range.
 5. The apparatus of claim 1 wherein the means for sustaining oscillation includes a pressurized gas source means responsive to the piston substantially minimizing one volume for applying a pressure pulse from the source to the cylinder to drive the piston in a direction tending to increase said one volume as the piston is moving in a direction to increase said one volume.
 6. The apparatus of claim 5 further including means for feeding pressurizing gas from one of the volumes to the pressurized gas source.
 7. The apparatus of claim 1 wherein the means for feeding hot fluid includes a hot chamber in the by-pass.
 8. The apparatus of claim 1 wherein the means for feeding cool fluid includes a cold chamber in the by-pass.
 9. The apparatus of claim 1 wherein the means for feeding hot fluid comprises a hot chamber in the by-pass and the means for feeding cold fluid comprises a cold chamber in the by-pass.
 10. The apparatus of claim 1 wherein the means for feeding hot fluid includes means for heating one of the volumes.
 11. The apparatus of claim 1 wherein the means for feeding cold fluid includes means for cooling the other of said volumes.
 12. The apparatus of claim 1 further including means for connecting a load to be responsive to fluid being decompressed as the piston coasts through the by-pass in a direction to decrease the first volume.
 13. The apparatus of claim 1 further including means for connecting a load to be responsive to gas being compressed as the piston coasts through the by-pass in a direction to decrease the second volume.
 14. The apparatus of claim 1 further including means for feeding gas pressure variations from one of said volumes to a load as the piston coasts through the region, and means for modulating a characteristic of the pressure variations.
 15. The apparatus of claim 14 wherein the means for modulating includes means for controlling the average pressure of gas in the cylinder.
 16. The apparatus of claim 14 wherein the means for modulating includes means responsive to a characteristic of the load for controlling the average pressure of gas in the cylinder.
 17. The apparatus of claim 14 wherein the means for modulating includes means for controlling the amplitude of the pressure variations.
 18. The apparatus of claim 14 wherein the means for modulating includes means responsive to a characteristic of the load for controlling the amplitude of the pressure variations.
 19. The apparatus of claim 14 wherein the means for modulating includes means for controlling the frequency of the pressure variations.
 20. The apparatus of claim 14 wherein the means for modulating includes means responsive to a characteristic of the load for controlling the frequency of the pressure variations.
 21. The apparatus of claim 14 wherein the means for modulating includes means for controlling the amplitude and frequency of the pressure variations.
 22. The apparatus of claim 14 wherein the means for modulating includes means responsive to a pair of characteristics of the load for controlling the amplitude and frequency of the pressure variations.
 23. The apparatus of claim 14 wherein the means for modulating includes means for varying a property of the by-pass.
 24. The apparatus of claim 14 wherein the means for modulating includes means for varying the length of the by-pass.
 25. The apparatus of claim 14 wherein the means for modulating includes means for varying the position of the by-pass along the length of the cylinder.
 26. The apparatus of claim 14 wherein the means for modulating includes means for varying the temperature of the fluid fed into one of the volumes.
 27. The apparatus of claim 26 wherein the by-pass includes means for changing the temperature of fluid in the by-pass, said temperature changing means being connected with said regenerator means and means for controlling the relative fluid flow between the temperature changing means and the regenerator means.
 28. The apparatus of claim 27 wherein the temperature changing means includes a heating chamber.
 29. The apparatus of claim 27 wherein the temperature changing means includes a cooling chamber.
 30. The apparatus of claim 27 wherein the temperature changing means includes means for heating the fluid in the by-pass, and means for cooling the fluid in the by-pass, said regenerator means including a regenerator chamber between the heating means and the cooling means.
 31. The apparatus of claim 30 wherein the flow control means includes means for separately controlling the relative fluid flows through the heating means and the cooling means.
 32. The apparatus of claim 27 wherein the regenerator means includes a first regenerator chamber connected in seriatim with the temperature changing means to form a first fluid flow path, and a second regenerator chamber connected in shunt with at least a portion of the first fluid flow path, said means for controlling including means for controlling the relative fluid flow between the second regenerator chamber and at least a portion of the first fluid flow path.
 33. The apparatus of claim 27 wherein the regenerator means includes a Regenerator chamber connected in seriatim with the temperature changing means, said means for controlling including a variable flow fluid path around the temperature changing means.
 34. The apparatus of claim 14 wherein the means for sustaining oscillation comprises thermal lag means having an inlet communicating with one of the volumes while the one volume has values in a minimum range, wherein the means for modulating includes means for controlling a property of the thermal leg device.
 35. The apparatus of claim 14 wherein the means for sustaining oscillation comprises thermal lag means having an inlet communicating with one of the volumes while the one volume has values in a minimum range, wherein the means for modulating includes means for controlling the volume of the thermal lag device.
 36. The apparatus of claim 14 wherein the means for sustaining oscillation comprises thermal lag means having an inlet communicating with one of the volumes while the one volume has values in a minimum range, wherein the means for modulating includes means for controlling the geometry of the thermal lag device.
 37. The apparatus of claim 14 wherein the means for sustaining oscillation comprises thermal lag means having an inlet communicating with one of the volumes while the one volume has values in a minimum range, wherein the means for modulating includes means for controlling the portion of the cycle that the thermal lag device is operative.
 38. The apparatus of claim 14 wherein the means for modulating includes means for varying the stiffness of gaseous spring means included in at least one of the volumes.
 39. The apparatus of claim 1 further including a port in a side wall of the cylinder for feeding gas from the cylinder to a load, said port being blocked by the piston while one of the volumes is in the minimum range and being unblocked while the piston is coasting through the region.
 40. The apparatus of claim 39 including means for controlling the position of the port along the length of the cylinder.
 41. The apparatus of claim 39 including means for controlling the position of the port along the length of the cylinder so that the port is blocked by the piston substantially while the by-pass is restricted.
 42. The apparatus of claim 39 including means for controlling the position of the port along the length of the cylinder so that the port is blocked by the piston substantially while the by-pass is restricted and the port is not blocked by the piston while the piston coasts through the region.
 43. The apparatus of claim 1 further including means for changing the temperature of fluid from an external source of fluid, and wherein one of said means for feeding is responsive to fluid in said means for changing and said fluid is changed in temperature by the temperature changing means prior to being fed into the cylinder.
 44. The apparatus of claim 1 wherein at least one of the means for feeding includes means for feeding fluid from an external source of fluid.
 45. The apparatus of claim 44 further including check valve means for feeding fluid from the external source into the cylinder only in response to the pressure of the fluid in the external source exceeding the pressure of the fluid in the cylinder.
 46. The apparatus of claim 1 including means for feeding fluid from one of said volumes to a load as the piston coasts through the region, and wherein said means for feeding fluid into at least one of said volumes includes means for feeding fluid from the load.
 47. The apparatus of claim 46 further including check valve means for feeding fluid from the load into the cylinder only in response to the pressure of the fluid returning from the load exceeding the pressure of the fluid in the cylinder.
 48. The apparatus of claim 1 wherein at least one of the means for feeding includes means for varying the temperature of fluid flowing into the volume.
 49. The apparatus of claim 48 further including check valve means for feeding gas from the Temperature changing means into the cylinder only in response to the pressure of the fluid in the temperature changing means exceeding the pressure of the fluid in the cylinder.
 50. The apparatus of claim 1 further including check valve means for feeding fluid only in one direction between one of said volumes and a load as the piston coasts through the region.
 51. The apparatus of claim 1 further including a check valve means wherein fluid is pumped substantially in only one direction in a flow path through a load.
 52. The apparatus of claim 1 wherein the means for sustaining comprises a thermal lag heater including passageways open at one end to be responsive to fluid in one of said volumes and for supplying heated fluid to said one volume as the piston is moving in a direction to increase said one volume.
 53. The apparatus of claim 52 wherein the passageways are located in the piston.
 54. The apparatus of claim 52 wherein the passageways are located in the piston and are heated in response to the hot fluid fed to the cylinder.
 55. The apparatus of claim 1 further including means for controlling the portion of the piston oscillation cycle during which the piston coasts in the by-pass region.
 56. The apparatus of claim 1 further including means for feeding fluid from one of said volumes to a load as the piston coasts through the region, a second cylinder, a second free piston in the second cylinder, said second cylinder and second piston being responsive to pressure variations derived from said means for feeding fluid, said second piston dividing the second cylinder into third and fourth variable volumes, and means tending to center oscillation of the second piston.
 57. The apparatus of claim 56 wherein the means tending to center oscillation includes a by-pass between the third and fourth volumes.
 58. The apparatus of claim 56 further including a magnetic circuit comprising: a magnetic component included in the second free piston, whereby magnetic flux variations are induced in the magnetic circuit in response to oscillation of the second free piston.
 59. The apparatus of claim 58 further including coil means responsive to the magnetic flux variations for driving an electric load in response to the magnetic flux variations.
 60. The apparatus of claim 58 further including means for controlling the average pressure in both said cylinders.
 61. The apparatus of claim 1 wherein both of said volumes are substantially enclosed chambers.
 62. The apparatus of claim 1 wherein the means for sustaining oscillation comprises thermal lag means having an inlet communicating with one of the volumes while the one volume has values in a minimum range, and means for varying the time during each oscillation cycle while the thermal lag means is operative.
 63. An oscillating piston apparatus comprising a pair of cylinders, a different free piston in each of said cylinders dividing each of the cylinders into first and second variable volume chambers, means for providing a fluid flow path between the second chambers of each cylinder while volumes of both of the second chambers have values in a minimum range, means for sustaining synchronized oscillation of the pistons in the cylinders, by-pass means between the first and second chambers of each cylinder while the piston of the cylinder is moving through a predetermined region of the cylinder between the ends of the cylinder, a regenerator means in the by-pass means, means for each cylinder for restricting the by-pass while the volumes of the first and second chambers have values in a minimum range, means for each cylinder for feeding hot fluid into the first chamber, and means for each cylinder for feeding cold fluid into the second chamber.
 64. The oscillating piston apparatus of claim 63 further including means for controlling like properties of the by-pass in a like manner.
 65. The oscillating piston apparatus of claim 63 wherein the means for controlling includes means for adjusting the leNgths of the two by-passes so that they are substantially the same.
 66. The oscillating piston apparatus of claim 63 wherein the means for controlling includes means for adjusting the positions of the two by-passes so that they are substantially the same.
 67. The oscillating piston apparatus of claim 66 wherein the means for controlling further includes means for adjusting the lengths of the two by-passes so that they are substantially the same.
 68. The oscillating piston apparatus of claim 63 further including means for coupling pressure variations from both cylinders to a single load.
 69. The oscillating piston apparatus of claim 63 wherein each of said cylinders includes a port in its side wall, each of said ports being responsive to pressure variations in the respective cylinders while the pistons coast through the regions, and means for combining pressure variations at said ports in a conduit and for driving a load in response to the combined variations.
 70. The oscillating piston apparatus of claim 69 wherein the means for sustaining includes a common thermal lag heater connected to said second chambers.
 71. The oscillating piston apparatus of claim 69 further including means for together and in the same manner controlling the positions of said ports along the lengths of the cylinders.
 72. The oscillating piston apparatus of claim 71 further including means for controlling the lengths of the by-passes in synchronism with the positions of the ports.
 73. The oscillating piston apparatus of claim 71 further including means for controlling the positions of the by-passes in synchronism with the positions of the ports.
 74. The oscillating piston apparatus of claim 69 wherein the load comprises a second cylinder, a second free piston in the second cylinder responsive to pressure variations derived from the combining means, means for centering the second free piston, a magnetic circuit including: magnetic poles displaced along the walls of the second cylinder, and a magnetic component included in the second free piston whereby magnetic flux variations are induced in the magnetic circuit in response to oscillation of the second free piston.
 75. The oscillating piston apparatus of claim 69 wherein the load comprises an alternator, said alternator including a pair of second cylinders having ends connected together and to the combining means so as to be responsive to pressure variations in the combining means, each of said second cylinders including a second free piston responsive to pressure variations in the combining means so that the second free pistons of the pair of cylinders are synchronously driven in response to the pressure variations, means for centering each of the second free pistons, each of said second cylinders being in a magnetic circuit including: magnetic poles on the second cylinders, and a magnetic component included in the second free pistons whereby magnetic flux variations are induced in the magnetic circuit in response to oscillation of the second free pistons, and coil means responsive to the magnetic flux variations, whereby an a.c. voltage is induced in each coil means in response to oscillation of the second free pistons.
 76. The oscillating piston apparatus of claim 75 wherein the means for centering includes a by-pass in each second cylinder, said by-pass providing for each second free piston, a coasting region near the center of oscillation of the second pistsons.
 77. The apparatus of claim 75 wherein the means for sustaining includes a thermal lag heater communicating with said second chambers.
 78. The apparatus of claim 75 including means responsive to voltage supplied to a load to automatically vary a property of the apparatus so as to maintain a more constant voltage.
 79. The apparatus of claim 75 including means responsive to the frequency of electrical power supplied to a load to vary a property of the apparatus so as to maintain a substantially constant frequency of piston oscillation.
 80. The appaRatus of claim 75 including means responsive to load voltage and frequency to vary at least one property of the apparatus to maintain a more constant voltage and frequency
 81. An oscillating piston device comprising a cylinder, a free piston in said cylinder dividing the cylinder into first and second variable volume chambers, means for sustaining oscillation of the piston in the cylinder, said means for sustaining including a pressurized gas source, means responsive to the piston substantially minimizing the volume of the first chamber for applying a pressure pulse from the source to the cylinder to drive the piston in a direction tending to increase the volume of said first chamber as the piston is moving in a direction to increase the volume of said first chamber, and means for establishing a by-pass between the first and second chambers while the piston is moving through a predetermined region of the cylinder between ends of the cylinder.
 82. A system for supplying energy to a load comprising a source for deriving oscillatory gas pressure, said source including: a regenerative gas cycle piston device comprising a cylinder, a free piston in the cylinder dividing the cylinder into first and second variable volumes, a by-pass including regenerator means, said by-pass connecting disparate parts of the cylinder together, the length of the by-passed portion of the cylinder being at least equal to the piston length, means for sustaining oscillation of the piston in the cylinder, means for restricting the by-pass while at least one of the volumes has values in a minimum range, wherein the piston functions as a displacer piston while completely within the length and the same piston functions as a reversing piston while any portion of the piston is outside of said length.
 83. The system of claim 82 further including means for feeding hot fluid into the first volume, and means for feeding cold fluid into the second volume.
 84. The system of claim 83 wherein the means for sustaining includes a thermal lag heater connected to one of the volumes.
 85. The system of claim 82 wherein ports to the by-pass are provided in the cylinder side wall at both ends of said length, said ports being blocked and unblocked by said piston to form said restricting means.
 86. The system of claim 85 wherein the means for feeding cold fluid is connected to one of the ports and the means for feeding hot fluid is connected to the other of the ports.
 87. The system of claim 86 including an outlet port for driving a load, said outlet port being positioned on the cylinder side wall at substantially the same axial location as one of the by-pass ports and being blocked and unblocked by the piston.
 88. The system of claim 82 including an outlet port for driving a load, said outlet port being positioned on the cylinder side wall so that it is responsive to fluid in the cylinder while the piston is in said length and is blocked by the piston while one of the volumes is in the minimum range.
 89. In combination, a cylinder, a free piston in the cylinder, an independent source of oscillatory pressure variations, and means for feeding pressure variations of the source into the cylinder to drive the piston in the cylinder in an oscillatory manner.
 90. The combination of claim 89 wherein the cylinder is divided into a pair of variable volumes by the piston, and the means for feeding includes a port in a side wall of the piston, said port being positioned so that the pressure variations of the source as coupled to one of said volumes are increased in amplitude.
 91. The combination of claim 90 further including means for controlling the center of oscillation of the piston.
 92. The combination of claim 89 further including means for controlling the center of oscillation of the piston.
 93. The combination of claim 92 wherein the means for controlling includes a by-pass around a portion of the cylinder side wall.
 94. An oscillating piston apparatus comprising a closed cylinder, a free Piston in said cylinder dividing the cylinder into first and second variable volumes, means for sustaining oscillation of the piston in the cylinder, a by-pass between the first and second volumes such that the piston coasts through a region of the cylinder between ends of the cylinder, means for restricting the by-pass during the piston oscillation while at least one volume has a value in a minimum range, means for feeding cool fluid into the second volume, and means for feeding hot fluid into the first volume.
 95. The apparatus of claim 94 wherein the means for feeding hot fluid is in the by-pass.
 96. The apparatus of claim 94 further including a regenerator in the by-pass.
 97. The apparatus of claim 96 wherein the means for feeding hot fluid includes a hot body in heat exchange relationship with gas in the by-pass, whereby the hot body is cooled.
 98. The apparatus of claim 97 further including check valve means for feeding cold fluid from the second volume to the first volume via a path in heat exchange relationship with the hot body.
 99. The apparatus of claim 98 wherein the means for feeding cold fluid includes a cold body in heat exchange relationship with gas flowing in a circuit beginning and ending at the second volume, whereby the cold body is heated, and check valve means for controlling the flow of the fluid that is in heat exchange relationship with the cold body.
 100. An oscillating piston apparatus comprising a closed cylinder, a free piston in the cylinder dividing the cylinder into first and second variable volumes, a by-pass between the first and second volumes such that the piston coasts through a region of the cylinder between ends of the cylinder, a regenerator in the by-pass, a hot chamber located in the by-pass between the regenerator and the first volume, a cold chamber located in the by-pass between the regenerator and the second chamber, means for restricting the by-pass during the piston oscillation while at least one volume has values in a minimum range, an external source of oscillatory pressure variations connected to the cylinder such that oscillation of the piston is sustained and fluid flows in the by-pass in a direction from the hot chamber to the cold chamber at a higher average pressure than the average pressure of fluid flowing in the by-pass in the opposite direction, whereby the hot chamber is heated and the cold chamber is cooled by fluid flowing in the by-pass.
 101. The apparatus of claim 100 wherein the external source is connected to a port in an end wall of the cylinder.
 102. The apparatus of claim 100 wherein the external source is connected to a port in the side wall of the cylinder.
 103. The apparatus of claim 96 wherein the by-pass includes two parallel paths, one of said paths including said regenerator, the other of said paths including said means for feeding hot fluid.
 104. The apparatus of claim 96 wherein the means for feeding cold fluid includes a cold body in heat exchange relationship with gas flowing in a flow path beginning and ending at the second volume, whereby the cold body is heated, and check valve means for controlling the flow of the fluid that is in heat exchange relationship with the cold body.
 105. The apparatus of claim 96 wherein the means for feeding cold fluid includes a cold body in heat exchange relationship with gas flowing in a flow path beginning in one of said volumes and ending at the second volume, whereby the cold body is heated, and check valve means for controlling the flow of the fluid that is in heat exchange relationship with the cold body.
 106. The apparatus of claim 96 wherein the means for feeding hot fluid includes a hot body in heat exchange relationship with gas flowing in a flow path beginning in one of said volumes and ending at the first volume, whereby the hot body is cooled, and check valve means for controlling the flow of the fluid that is in heat exchange relationship with the hot body.
 107. The apparatus of claim 94 including regeneratoR means in the by-pass, wherein at least one of the means for feeding includes a gas flow path beginning at one of said volumes and ending at one of said volumes, check valve means for attaining a net flow in said path in one direction, and heat exchange means between an external body and gas flowing in the path.
 108. The apparatus of claim 1 wherein the piston is of integral construction.
 109. The apparatus of claim 1 wherein the piston has a substantially uniform cross section throughout substantially all of its length.
 110. The apparatus of claim 1 wherein the piston is of substantially integral construction and has a substantially uniform cross section throughout substantially all of its length.
 111. The apparatus of claim 1 wherein at least one of said volumes is a substantially closed chamber during a portion of the piston oscillation cycle while said one volume is in a minimum range to form a gaseous spring for reversing the direction of motion of the piston.
 112. The apparatus of claim 1 wherein the by-pass includes ports in the side wall of the cylinder for establishing fluid flow paths from the cylinder to the regenerator, and a further port in the side wall for establishing a fluid flow path from the cylinder to a device external to the cylinder.
 113. The apparatus of claim 112 wherein the further port is subsatntially aligned with one of the by-pass ports.
 114. The apparatus of claim 63 wherein each of the pistons is of substantially integral construction.
 115. The apparatus of claim 63 wherein each of the pistons has a substantially uniform cross section throughout substantially all of its length.
 116. The apparatus of claim 63 wherein the means for feeding fluid includes by-pass ports in the side wall of each cylinder for connecting the cylinder by-pass in fluid flow relation with the cylinder.
 117. The apparatus of claim 116 including at least one additional port in the wall of each cylinder for coupling pressure variations within the cylinder to a load.
 118. The apparatus of claim 117 further including means for connecting at least one of said additional ports of each cylinder together to couple pressure variations within each cylinder to a common load.
 119. The apparatus of claim 63 wherein the by-pass means includes a separate by-pass for each of the cylinders. 